Electrodeposition as a coating application method involves the deposition onto a conductive substrate of a film-forming composition under the influence of an applied electrical potential. Electrodeposition has gained popularity in the coatings industry because it provides higher paint utilization, outstanding corrosion resistance, and low environmental contamination as compared with non-electrophoretic coating methods. Both cationic and anionic electrodeposition are used commercially, with cationic being more prevalent in applications desiring a high level of corrosion protection. Anionic electrodeposition is typically used for decorative applications, particularly where low cost and decorative qualities such as gloss and color are desired. Electrodepositable cationic acrylic vehicles with optional minor amounts of cationic epoxy are typically used for applications in which both decorative and anti-corrosion properties are desirable.
There are a number of decorative applications in which it is desired to control the gloss of a coating layer applied by electrodeposition. E-coat compositions having high gloss levels are readily achievable, but compositions with a low gloss level that is retained after exterior exposure have been very hard to prepare. Addition of traditional flatting agents such as silicas and alumina silicates to E-coat compositions will produce the desired gloss levels initially, but the finishes discolor and chalk quickly upon exposure to the elements. Furthermore, traditional flatting agents are often much more dense than other bath components and will settle in the electrocoat baths; continuous recirculation must therefore be employed to maintain paint homogeneity, even when the bath is not in use. The need for continuous recirculation leads to higher capital equipment costs, higher maintenance costs, and higher energy costs.
Another issue that arises with electrocoat application is dirt removal. Metal parts being coated are invariably contaminated to one degree or another with particulate matter that can accumulate in the electrocoat tank. The particles must be removed to insure a defect-free paint finish. This is typically accomplished by continuous filtration of the electrocoat bath. Known flatting agents, especially organic flatting agents, interfere with this dirt removal process by fouling filtration equipment.